Filter for EGR system heated by an enclosing catalyst

ABSTRACT

A device and a method for exhaust gas purification in a combustion engine comprises an arrangement ( 30 ) for recirculating exhaust gases from the engine ( 1 ) to an air intake ( 2 ) thereof. An exhaust gas purification arrangement ( 31 ) is adapted to convert constituents in the exhaust gases to less environmentally hazardous substances. A filter arrangement ( 32 ) comprises at least one filter ( 33 ) adapted to liberate the exhaust gases from particulate constituents. This filter ( 33 ) is adapted to purify EGR-exhaust gases only. According to another aspect of the invention, 2 the filter ( 33 ) is aged in heat transferring relation to at least one convener unit ( 34 ) of the exhaust gas purification arrangement so as to receive, from the convener unit, a heat addition to promote regeneration of the filter by combustion of paniculate constituents deposited therein.

FIELD OF THE INVENTION AND PRIOR ART

This invention is related to a device for purifying exhaust gases from acombustion engine according to the precharacterizing part of enclosedclaim 1. Besides, the invention is related to a method for exhaust gaspurification and use of the device for exhaust gas purification inparticular at a diesel engine.

It is known that EGR (Exhaust Gas Recirculation) is an advantageouspurification method for reducing the proportion of hazardous exhaustgases, in particular nitrogen oxide (NO_(x)). In an EGR-system, a partof the exhaust gases from the engine are recirculated to an air intakethereof.

It is also known to use exhaust gas purification arrangements comprisingat least one converter unit for converting constituents of the exhaustgases to less environmentally hazardous substances. According to thepresent state of the art, such converter units comprise, generally,catalysts for achieving a catalytic conversion of constituents in theexhaust gases to less environmentally hazardous substances. Thus, bymeans of such catalysts, carbon monoxide and hydro carbons may beconverted to carbon dioxide and water. This presupposes that the exhaustgases contain a certain amount of oxygen. For this purpose an oxygenmeasuring unit is generally used in the exhaust gas flow from the engineand this unit delivers output signals, on basis of which the operationof the engine is controlled to achieve the required oxygen contents.Furthermore, also nitrogen oxides may be converted to neutral nitrogenby means of such catalysts. An excess of oxygen in the exhaust gaseswould give rise to cessation of the reduction of nitrogen oxides whereasa deficiency with respect to oxygen would counteract conversion of theother constituents mentioned above in the exhaust gases. An optimalregulation of the fuel system may, however, cause a decrease of allabove mentioned, hazardous constituents. By using EGR technique, afurther reduction of nitrogen oxides may be achieved.

In addition, there exists the problem, in particular in diesel engines,that they generate a substantial amount of particulate constituents.Within the framework of the expression particulate constituents thereare included both particles as such, for instance soot, and organicresidues (denominated SOF) which emanate from fuel and oil. It is knownto use filters of various types to liberate the exhaust gases from suchparticulate constituents. It is also known to design such filters asregenerating, i.e. that they may be restored without exchange. Suchregeneration is according to the prior art achieved by heating thefilters to a required degree so that combustion of the particulateconstituents occurs. The energy requirement for such combustion is verylarge, for what reason one has had, according to the prior art, toimmobilise the filter, either still coupled to the engine or removedtherefrom so that by connection of a heating element to an electricpower network the required heating may occur. Thus, this necessitatesan, interruption of operation. Another technique (U.S. Pat. No.5,207,734 and JP 8338320) to achieve regeneration of a filter in an EGRrecirculation conduit is to use a catalyst upstreams of the filter toprovide for a heat addition to the filter from the catalyst. However,this results in deficient filter regeneration, in particular when therecirculated exhaust gas amount is small as it is under some engineoperating conditions.

SUMMARY OF THE INVENTION

The object of the present invention is to develop the prior art for thepurpose of achieving efficient filter regeneration and efficientpurification with regard to NO_(x), carbon monoxide, hydro carbons,particles etc.

This object is achieved by the features of enclosed claim 1.

The present invention is, accordingly, based upon the idea to arrangethe filter so that heat in the exhaust gases and in addition the heatwhich occurs as a consequence of the conversion in the converter unitmay be transversely transported from the converter unit to the filter sothat the conditions for regeneration of the filter are substantiallyimproved. It is pointed out that in EGR systems, the recirculatedexhaust gas volume varies depending upon the operational conditions ofthe engine. During some conditions small volumes per time unit pass thefilter. The heating requirement of the filter for regeneration may thennot be satisfied by the heat in the exhaust gases flowing through thefilter only. According to the invention it is possible to reach suchhigh temperatures of the filter that only a comparatively small heataddition, if any, is required in order to achieve, also under difficultoperational conditions, the necessary filter regeneration, i.e.combustion of particulate constituents deposited in and on the filter.More specifically, conditions are in this way created to bring thefilter to the necessary regeneration temperatures by means of one ormore heating elements having a relatively low effect. The energy supplyto such heating elements does not become higher than making electricsystems provided on e.g. vehicles capable of producing the energygeneration.

Further preferable embodiments of the invention are dealt with in therest of the claims and in the following description.

The method according to the invention and use of the device are recitedin the enclosed claims.

BRIEF DESCRIPTION OF THE DRAWINGS

With reference to the enclosed drawings, a more specific description ofembodiment examples of the invention will follow hereafter.

In the drawings:

FIG. 1 is a principle drawing showing an engine installation withexhaust gas purification according to the invention;

FIG. 2 is a partly cut view illustrating the arrangement according tothe invention of a converter unit and a filter;

FIG. 3 is a perspective view of that which appears in longitudinalsection in FIG. 2; and

FIG. 4 is a view similar to FIG. 2 and illustrating the principle of analternative embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 illustrates diagrammatically the device according to theinvention in the form of an engine installation and exhaust gaspurification applied thereto. The combustion engine is diagrammaticallyindicated at 1. Air is taken thereto via an air intake 2, in connectionwith which an air filter 2 a may be provided. The air is directed via aninlet air channel generally denoted 3 towards combustion chambers of theengine. It is already now pointed out that the present invention isapplicable to engines operating by suction only, i.e. where the airtransport into the combustion chamber of the engine is generated bysuction due to piston movements in the engine. However, the invention isalso applicable to supercharging, i.e. forced air supply to the engine,which generally can be accomplished by means of a compressor. Such acompressor may be driven in an arbitrary manner, e.g. mechanically viathe engine or suitable auxiliary equipment or, as indicated in FIG. 1,by means of the exhaust gas flow from the engine. Thus, the devicecomprises in the example a turbo charger 4, comprising a compressorwheel 4 a for feeding the air to the engine with over-pressure and aturbine wheel 4 b placed so as to be put into rotation by actuation ofexhaust gases leaving the engine. The compressor wheel 4 a and theturbine wheel 4 b are operationally coupled to each other, e.g. by beingplaced on one and the same axle. As is usual in supercharging, the airmay be subjected to cooling, after having been imparted anover-pressure, in a charging air cooler 5 (intercooler). The exhaustgases exiting the engine move in an exhaust pipe 6 and enter into thesurroundings via an exhaust gas outlet 9.

As will be described in more detail in the following, the devicecomprises an arrangement generally denoted 30 for recirculating exhaustgases from the engine to the air intake 2 of the engine. For thispurpose there is a recirculation conduit denoted 10. This is in theexample connected to the inlet air channel denoted 3. If required, therecirculation conduit 10 may pass through a cooler 11 to cool down therecirculated exhaust gases. The conduit 10 may adjoin to the inlet airchannel 3 via a valve arrangement 12, which is controllable by means ofan EGR control arrangement 13. The valve arrangement 12 may, by means ofthe EGR control arrangement 13, regulate the relation between the amountof supplied fresh air from the inlet air channel 3 and the suppliedamount of recirculated exhaust gases from the recirculation conduit 10.This mixture adjusted by means of the valve 12 may, accordingly, besupplied to the air intake 2 of the engine.

The EGR control arrangement 13, which controls the valve device 12, issupplied with information about the actual state of operation of theengine from a.o. an oxygen measuring probe (lambda probe) 14, a sensor15 for the number of revolutions of the engine and a sensor 16 forthrottle position. The EGR control arrangement 13 is programmed tocontrol the valve device 12 and, accordingly, the mixing relation freshair/exhaust gases for the purpose of minimising the contents ofhazardous substances leaving the exhaust gas outlet 9 and being releasedinto the free air. The programming of the EGR control arrangement 13occurs in a manner known perse to achieve a favourable relation betweenthe various factors mentioned above.

The valve arrangement 12 could of course comprise separate valves in theinlet air channel 3 and in the recirculation channel 10, said valvesthen being separately controllable by the EGR control arrangement 13.Alternatively, the valve arrangement 12 may also comprise a unit, inwhich flows from the inlet air channel 3 and the recirculation conduit10 may be selectively brought together, by means of valves included inthe valve arrangement, to a common output flow, which is directedfurther towards the air intake 2 of the engine.

The device according to the invention-further comprises an exhaust gaspurification arrangement generally denoted 31 and adapted to convertconstituents in the exhaust gases to less hazardous substances.Furthermore, the device comprises a filter arrangement generally denoted32 and adapted to liberate the exhaust gases from particulateconstituents.

The filter arrangement 32 comprises at least one filter 33 arranged inheat transferring relation to at least one converter unit 34 of theexhaust gas purification arrangement 31 for receiving, from theconverter unit, a heat addition for promoting regeneration of the filter33 by combustion of particulate constituents deposited therein.

It appears diagrammatically from FIG. 1 that both the exhaust gaspurification arrangement 31 and the filter arrangement 32 are conceivedto be placed in a common casing 35 located in such a way in the exhaustpipe 6 that the casing in a manner described hereinafter will have aflow through the same of exhaust gases leaving the engine.

FIGS. 2 and 3 illustrate in a larger scale the casing 35 appearing fromFIG. 1 and the components present therein. The intended flow directionof exhaust gases is indicated with the arrow 36 in FIG. 2. Thus, theexhaust gases from the engine arrive at the right side in both FIGS. 2and 3.

The filter 33 is arranged in a first flow path 37 adapted to recirculateexhaust gases to the air intake 2 of the engine. More specifically, thisflow path 37 comprises a pipe piece 38 included in the recirculationconduit 10 previously mentioned. The pipe piece 38 is illustrated, inthe example, as being bent and directed obliquely out through the casing35.

The converter unit 34 is arranged in a second flow path 39, in whichexhaust gases flow from the engine to the exhaust gas outlet 9 (FIG. 1)communicating with the surroundings. The first and second flow paths 37,39 are adapted to receive and have flowing through the same differentexhaust gas flows received from the engine (arrow 36). Expressed inother words, the flow paths 37, 39 may be said to be arrangedtransversely overlapping and in parallel. In the example according toFIGS. 2 and 3, mouths 40 and 41 of the first and second flow paths 37and 39 respectively are arranged so as to face arriving exhaust gases.

FIG. 4 illustrates a variant in this regard. Here it is indicated withthe arrows 36 how exhaust gases arrive from the engine. These exhaustgases first flow through the second flow path 39′. A part of the exhaustgases having passed the converter unit 34′ then moves into the firstflow path 37′ according to the arrows 42. The main part of the exhaustgas flow proceeds in accordance with the arrow 43 towards the exhaustgas outlet 9. As in the preceding case, the pipe piece 38′ is coupled tothe recirculation conduit 10 according to FIG. 1. In summary, theconverter unit 34′ will have flowing through the same, in the variantaccording to FIG. 4, the entire exhaust gas flow whereas then a part ofthis exhaust gas flow will pass through the filter 33′.

Common to the embodiments according to FIGS. 2-4 is that the filter 33is at least partly enclosed by the converter unit 34. More specifically,the embodiment is such in the example that the converter unit 34 iscross-sectionally substantially ring shaped whereas the filter 33 isarranged within this ring. In the example the converter unit has asubstantially hole-cylindrical shape whereas the filter 33 iscylindrical.

In the embodiment according to FIG. 4, the mouth 40′ of the first flowpath 37′ is located downstreams the converter unit 34′ present in thesecond flow path 39′ in contrast to the embodiment according to FIGS. 2and 3, where the filter 33 and the converter unit 34 are parallel andtransversely overlappingly arranged so that the mouths 40, 41 of theirflow paths are situated generally in the same plane.

A heating element 44 is adapted to supply additional heat to the exhaustgases passing through the filter 33. The heating element 44 is adaptedto heat only those exhaust gases being recirculated to the engine. Thus,the heating element 44 is arranged in the first flow path 37 upstreamsof at least a part of the filter. More specifically, the heating element44 is suitably arranged at the mouth 40 of the flow part 37.Corresponding comments are also applicable with regard to the embodimentaccording to FIG. 4 although, as appears from the preceding description,the heating element 44′ will be located at that end of the converterunit 34′ which is located downstreams as concerns the total exhaust gasflow according to the arrows 36.

It is preferred that the heating element 40 is electric. The operationof the heating element is preferably controlled by a control unitobtaining temperature information as to temperatures of the exhaustgases flowing in the recirculation conduit 10 back to the air intake ofthe engine so that accordingly the heating element may be caused tooperate for achieving the desired temperature in the filter 33 proper.Instead of sensing the temperature in the recirculation conduit 10, atemperature sensor could of course also be integrated into the filter 33proper or placed in the vicinity thereof.

The converter unit 34 comprises suitably a catalyst. This term refers tosuch a structure having a catalytical action such that exhaust gasesflowing by may be converted catalytically so as to cause transfer ofconstituents in the exhaust gases to less environmentally hazardoussubstances. This gives rise to at least some heat addition in theconverter unit 34. It is the heat of the exhaust gases and this heataddition that are intended to be, at least partially, communicated tothe filter 33 in heat transferring relation to the converter unit 34.

As to the catalyst structure 34, it is pointed out that the same, thus,is formed by an oxidation catalyst, the ability of liberating theexhaust gases from particulate constituents being lower than that of atrue filter but nevertheless important, e.g. in the order of 30-40%depending upon the nature of the particulate constituents. The catalyststructure 34 is normally prepared such that a suitable large-surfacebase material is coated with the true catalyst material, e.g. a preciousmetal.

The catalyst structure 34 may be secured relative to the casing 35 bymeans of suitable mechanical connection members 45.

The filter 33 comprises a material resistant to high temperatures andhaving a good filtrating ability. As an example ceramic materials,mineral fibres and metallic fibres may be mentioned as useful. Theselected material must withstand the high temperatures that may arise onregeneration of the filter. It is preferred that the filter 33 and theconverter unit 34 are separated by a tubular element 46, at one end ofwhich the heating element 44 is located and the other end of which isconnected to the pipe piece 38. The tubular element 46 may be connectedto the surrounding converter unit 34 by means of securing elements47.The filter 33 and cenverter unit 34 should be interrelated such thatefficient heat transfer between them may occur by heat conduction and/orradiation.

It is pointed out that it would be possible to have the filter 33 carryout a dual function. Thus, the filter material could be provided withcatalytic material so that also a catalytic conversion of constituentsin the exhaust gases would occur in the filter.

The embodiment according to FIGS. 2 and 3 operates in the followingmanner: when the engine 1 is running, exhaust gases arrive according tothe arrow 36 to the interior of the casing 35. A part of the exhaustgases passes through the converter unit 34 and is catalyticallyconverted therein at the same time as the unit is capable of removing atleast a part of the particulate constituents accompanying the exhaustgases and these particulate constituents are combusted in the unit 34 sothat a regeneration occurs also with regard to this “filtration effect”in the converter unit 34.

Another part of the exhaust gases arriving according to the arrow 36reaches into the flow path 37 and passes therein through the filter 33and is liberated from particulate constituents. This part flow of theexhaust gases is recirculated via the recirculation conduit 10 to theair intake of the engine so that an EGR function arises withaccompanying favourable effects with regard to exhaust gas purification.The filter 33 is highly efficient for filtration purposes and istypically capable of removing more than 90% of the particulateconstituents from the exhaust gases. These constituents are deposited onthe filter material. The filter material will be heated as a consequenceof the heat in the exhaust gases and the combustion process in thesurrounding catalyst material so that the filter 33 achieves afavourably raised temperature than otherwise. This increased temperatureis used for regeneration of the filter, i.e. combustion of theparticulate constituents deposited therein. This combustion may bepromoted, if required by the circumstances, by increasing, by means ofthe heating element 44, the temperature of the exhaust gases passing theheating element 44 and reaching into the filter 33. By a suitabletemperature sensing, an optimum regulation of the temperature in thefilter 33 may be achieved. It is in this connection pointed out thatregeneration of the filter 33 may occur continuously as well asintermittently.

It is again pointed out that it is possible, at least in part, toprovide the filter 33 with a catalysing aspect so that filterregeneration may be carried out at a lower temperature than that whichotherwise would be necessary. However, it is pointed out that it is thefiltrating effect of the element 33 which is of primary interest; thementioned catalyst effect is only secondary.

The function is in all essentials the same in the embodiment describedin FIG. 4 with the exception that there the exhaust gases having passedthe converter unit 34′ are those which also to a part will pass throughthe filter 33′.

It is emphasised that the invention described in no way is limited onlyto that which has been described above. Although the invention isparticularly preferable with diesel engines, it is pointed out that thesame also may be used with other engine types. Furthermore, it ispointed out that of course other arrangements of filters 33 andconverter units 34 are possible to realise by the man skilled in the artwhen the basic concept of the present invention has been presented.Thus, a plurality of filter elements could of course be provided andthese filter elements could be distributed in one or more bodies of theconverter unit 34, i.e. that it is not necessary that thefilter/converter unit 34 are concentric. The important thing for thisaspect of the invention is that the filter 33 and the converter unit 34are present in such mutual heat transferring connection that the filter33 will be heated by the converter unit 34. As an example, the filter 33could be arranged to enclose the converter unit 34 instead of theopposite. Also other modifications are possible within the scope of theinvention.

What is claimed is:
 1. A device for purifying exhaust gases from acombustion engine (1), comprising an arrangement (30) for recirculatingexhaust gases from the engine to an air intake (2) thereof, an exhaustgas purification arrangement (31) adapted to convert constituents in theexhaust gases to less environmentally hazardous substances and a filterarrangement (32) adapted to liberate the exhaust gases from particulateconstituents, the filter arrangement (32) comprising at least one filter(33) arranged to receive from at least one converter unit (34) of theexhaust gas purification arrangement (31) a heat addition to promoteregeneration of the filter by combustion of particulate constituentsdeposited therein, the filter (33) and the converter unit (34) beingarranged in at least partly overlapping heat transferring relation asviewed transversely to the direction of exhaust gas flow, characterizedin that the filter (33) is arranged in a first flow path (37) adapted torecirculate exhaust gases to the air intake (2) of the engine, and theconverter unit (34) is arranged in a second flow path (39), in whichexhaust gases flow from the engine (1) to an exhaust gas outlet (9)communicating with the surroundings.
 2. A device according to claim 1,characterized in that the first and second flow paths (37, 39) arearranged to receive, from the engine, and have flowing throughthemselves separate exhaust gas flows.
 3. A device according to claim 1,characterized in that the second flow path (39′) is arranged to haveflowing through the same at least one part exhaust gas amount, whichthereafter flows through the first flow path (37′).
 4. A deviceaccording to claim 1, characterized in that one of the filter (33) andthe converter unit (34) at least partly encloses the other of saidfilter and converter unit.
 5. A device according to claim 4,characterized in that the filter (33) is at least partly enclosed by theconverter unit (34).
 6. A device according to claim 5, characterized inthat the converter unit (34) is cross-sectionally substantially ringshaped and that the filter (33) is arranged with this ring.
 7. A deviceaccording to claim 2, characterized in that mouths (40,41) of the firstand second flow paths (37, 39) are arranged so as to face arrivingexhaust gases.
 8. A device according to claim 1, characterized in thatthe mouth (40′) of the first flow path (37′) is located downstream theconverter unit (34′) present in the second flow path (39′).
 9. A deviceaccording to claim 1, characterized in that the heating element (44) isadapted to supply additional heat to the exhaust gases passing throughthe filter (33).
 10. A device according to claim 9, characterized inthat the heating element (44′) is adapted to heat only those exhaustgasses which are recirculated to the engine.
 11. A device according toclaim 9, characterized in that the heating element (44) is arranged inthe first flow path (37) upstream of at least a part of the filter (33).12. A device according to claim 9, characterized in that the heatingelement (44) is electric.
 13. A device according to claim 9,characterized in that the converter unit (34) comprises a catalyst. 14.A device according to claim 1, characterized in that the filter (33)comprises a material resistant to high temperatures and having a goodfiltering capacity.
 15. A device according to claim 1, characterized inthat the first flow path (37) is connected to an exhaust pipe of thedevice either upstream or downstream of the converter unit (34) arrangedin the exhaust pipe.
 16. A device according to claim 1, characterized inthat the first flow path (37) containing the filter (33) is connected toan exhaust pipe (6) of the device downstream of a turbo charger turbineplaced in the exhaust gas stream.
 17. Use of a device according to claim1, for purification of exhaust gases from diesel engines.
 18. A deviceaccording to claim 2, characterized in that the heating element (44) isadapted to supply additional heat to the exhaust gases passing throughthe filter (33).
 19. A device according to claim 3, characterized inthat the heating element (44) is adapted to supply additional heat tothe exhaust gases passing through the filter (33).
 20. A deviceaccording to claim 4, characterized in that the heating element (44) isadapted to supply additional heat to the exhaust gases passing throughthe filter (33).
 21. A device according to claim 1, wherein said firstflow path (37) containing said filter (33) and second flow path (39)containing said converter unit (34) are arranged in superimposed,overlapping relationship adjacent one another in said transversedirection to the direction of exhaust gas flow (36).
 22. A deviceaccording to claim 21, wherein said first and second flow paths (37, 39)are arranged transversely overlapping and in parallel.
 23. A deviceaccording to claim 1, wherein said first and second flow paths (37, 39)are separated from one another and form separate and distinct flow pathsfrom one another.
 24. A device according to claim 7, wherein said firstflow path (37) containing said filter (33) is concentrically arrangedwithin said second flow path (39) containing said converter unit (34),with said filter (33) and converter unit (34) being adjacent one anotherin said transverse direction to exhaust gas flow (36), a tubular element(46) separating said filter (33) and converter unit (34) from oneanother, with said mouths (40, 41) of said respective flow paths (37,39) being generally situated in the same transverse plane, and saidfirst flow path (37) communicating with said recirculating arrangement(30) through a bent pipe (38) directed obliquely out through a casing(35) comprising said filter (33) and converter unit (34), such that aportion of exhaust gases (36) entering an interior of said casing (35)pass through said converter unit (34) and are exhausted (9), whileanother portion of the exhaust gases (36) arriving into said container(35) pass into said first flow path (37), through said filter (33) andback to said combustion engine (1) along said recirculating arrangement(30).
 25. A device according to claim 22, wherein said filter (33) is atleast partially enclosed by said converting unit (34) with said filter(33) being substantially cylindrically shaped, and said converter unit(34) being substantially cross-sectionally ring shaped.
 26. A deviceaccording to claim 23, wherein said mouth (40′) of said first flow path(37′) is located downstream of said converter unit (34′) present in saidsecond flow path
 27. A device according to claim 1, additionallycomprising a tubular element (46) separating said filter (33) andconverter unit (34) in said transverse direction.
 28. A device accordingto claim 1, wherein said filter (33) and converter unit (34) remain incontinuous heat transferring relation as said exhaust gasessimultaneously flow through both said first and second flow paths (37,39).
 29. A device according to claim 28, wherein said converter unit(34) is cross-sectionally substantially ring-shaped with said filter(33) arranged within this ring and being substantially cylindrical. 30.A device for purifying exhaust gases from a combustion engine(1),comprising an arrangement (30) for recirculating exhaust gases fromthe engine to an air intake (2) thereof, an exhaust gas purificationarrangement (31) adapted to convert constituents in the exhaust gases toless environmentally hazardous substances and a filter arrangement (32)adapted to liberate the exhaust gases from particulate constituents, thefilter arrangement (32) comprising at least one filter (33) arranged toreceive from at least one converter unit (34) of the exhaust gaspurification arrangement (31) a heat addition to promote regeneration ofthe filter by combustion of particulate constituents deposited therein,the filter (33) and the converter unit (34) being arranged in at leastpartly overlapping heat transferring relation as viewed transversely tothe direction of exhaust gas flow, characterized in that the filter (33)is arranged in a first flow path (37) adapted to recirculate exhaustgases to the air intake (2) of the engine, the converter unit (34) isarranged in a second flow path (39), in which exhaust gases flow fromthe engine (1) to an exhaust gas outlet (9) communicating with thesurroundings, a mouth (40′) of the first flow path (37′) is locateddownstream of the converter unit (34′) present in the second flow path(39′), said first flow path (37′) containing said filter (33′) comprisesa mouth (40′) opening in a direction facing away from incoming exhaustgas flow (36), with said first flow path (37′) situated concentricallywithin said second flow path (39′) comprising said converter unit (34′)which is concentrically situated about said filter (33′), and said firstflow path (37′) communicates with said recirculating arrangement (30)through a bent pipe (38′) directed obliquely out through a casing (35)containing said exhaust gas purification arrangement (31), such thatexhaust gases (36) flowing from said combustion engine (1) entirely flowthrough said converter unit (34′) situated in said second flow path(39′), with a portion of said exiting exhaust gas reversing direction(42) and flowing back into said first flow path (37′) and through saidfilter (33′).
 31. A device for purifying exhaust gases from a combustionengine (1), comprising an arrangement (30) for recirculating exhaustgases from the engine to an air intake (2) thereof, an exhaust gaspurification arrangement (31) adapted to convert constituents in theexhaust gases to less environmentally hazardous substances and a filterarrangement (32) adapted to liberate the exhaust gases from particulateconstituents, the filter arrangement comprising at least one filter (33)arranged to receive from at least one converter unit (34) of the exhaustgas purification arrangement (31) a heat addition to promoteregeneration of the filter by combustion of particulate constituentsdeposited therein, the filter (33) and the converter unit (34) beingarranged in overlapping heat transferring relation as viewedtransversely to the direction of exhaust gas flow, characterized in thatthe filter (33) is arranged in a first flow path (37) adapted torecirculate exhaust gases to the air intake (2) of the engine, theconverter unit (34) is arranged in a second flow path (39), in whichexhaust gases flow from the engine (1) to an exhaust gas outlet (9)communicating with the surroundings, and said filter (33) in said firstflow path (37) back to the engine and said converter unit (34) in saidsecond exhaust flow path (39) are arranged in complete superimposedoverlapping relationship adjacent one another in said transversedirection to exhaust gas flow, with said filter (33) and converter unit(34) remaining in continuous heat transfer relation as said exhaustgases simultaneously flow through both said first and second flow paths(37, 39).
 32. A device according to claim 31, wherein said converterunit (34) is cross-sectionally substantially ring-shaped with saidfilter (33) arranged within this ring and being substantiallycylindrical.